1. Field of the Invention
The present invention relates to an electron tube.
2. Related Background Art
U.S. Pat. No. 5,374,826 discloses an electron tube with a housing including a window, a sidewall, and an electrode. In this electron tube, due to radioactive impurities contained in ceramic being a material of the sidewall, a minute quantity of radiation is emitted. Moreover, in the electron tube, borosilicate glass is often used as a material of the window and housing, and metal is used as a material of the electrode. Radioactive impurities contained in the borosilicate glass, metal, etc., also emit a minute quantity of radiation.
In, for example, an observational experiment of dark matter, an observational experiment of various cosmic rays, etc., using a scintillator that emits light upon incidence of radiation, since a signal light itself from a detection target is often weak, it is necessary to reduce noise as much as possible. Here, when an electron tube that converts light from a scintillator to electrons is used for detection, a light emission due to a minute quantity of radiation generated from the electron tube itself results in noise.